The present disclosure relates generally to methods and systems for optical communications in a wellbore environment. Hydrocarbons, such as oil and gas, are commonly obtained from subterranean formations that may be located onshore or offshore. The development of subterranean operations and the processes involved in removing hydrocarbons from a subterranean formation typically involve a number of different steps such as, for example, drilling a wellbore at a desired well site, treating the wellbore to optimize production of hydrocarbons, and performing the necessary steps to produce and process the hydrocarbons from the subterranean formation.
Upon drilling a wellbore that intersects a subterranean hydrocarbon-bearing formation, a variety of downhole tools may be positioned in the wellbore during exploration, completion, production, and/or remedial activities. For example, sensor components may be lowered into the wellbore during drilling, completion, and production operating phases of the wellbore. Sometimes the sensors are coupled to communication systems for conveying data indicative of sensed downhole parameters from the downhole sensor component to a surface location. For example, the downhole system (e.g., wireline, slickline) may include a fiber optic communication system for relaying sensed parameter measurement data from the downhole sensor to the surface for evaluation in near real time or real time. Optical communication systems may also be designed to provide downgoing signals from the surface to downhole tools.
In existing optical communication systems, an optical fiber is typically used to guide and propagate light waves from a source to a receiver (or detector). Due to the often harsh conditions downhole (e.g., high temperature and pressure), it is generally preferable to have only simple and robust components downhole. Accordingly, optical sources and detectors are often positioned at the surface of the wellbore instead of downhole. However, this requires that optical signals travel downhole and then return. Typical optical communications systems of this type have a u-bend or mini-bend downhole. However, such systems require twice as much optical fiber and significant space for the curved fiber, increasing the cost and size of the optical system. Further, such systems must be shielded from the wellbore environment by a protective sheath or jacket as they may be susceptible to high temperatures and pressures.
Optical communication systems often use reflectors such as fiber bragg gratings to reflect optical signals. However, typical reflectors are susceptible to downhole temperatures and pressures, reflect only a narrow band of wavelengths, or require specialized optical fibers.
Distributed sensing systems are used downhole to determine a parameter along the length of a fiber. For example, double-ended distributed temperature sensing employs a double-ended optical fiber to measure temperature over the length of an optical fiber. However, such systems take up a significant amount space in a crowded wellbore and rely on complex time division techniques to determine the profile of a downhole condition.